AWD Transmission: XC 90 wont reverse up hill

[Tannaton]

The problem is that the chaps at the dealers will be following a flow chart type diagnosis - that's they way they are told to work - and for this really obscure scenario there probably is no flow chart.

The above will work in 98% of circumstances to give the Volvo customer a good service, but in 1% - 2% like these - it has the opposite impact.

This is where you need to understand the cars and the systems.

I personally think it is likely wear or a defect in one of the front hubs which is causing either the driveshaft splines to slip in reverse under throttle or erroneous readings from the wheel sensors. In that case all systems are working normally - no fault codes - but they are making decisions to override commanded throttle based on erroneous information. Add to the as the driver is reversing - looking through the rear window - they won't notice the traction control light flashing on the dash. It's just this sort of complex system problem where multiple small, insignificant issues interact with each other to create a situation where there is no logical explanation, but once diagnosed is very simple to explain in hindsight. This is why 2 737-Max aircraft crashed and it had to be grounded.

And this is why I love working with these cars - I buy cars like this with obscure problems that no dealer can seemingly fix and I fixed them, I spend 80% of my time reading and observing - and it's usually a £50 sensor or a broken wire etc.

Clearly this fault might by why the previous owner sold it - I do hope he finds a "spanner man" to work with him and I expect it will be a cheap fix (cheaper than a new gearbox that he didn't need anyway).

[removaldaddy]

Well done you for that suggestion

[Tannaton]

Did you get this sorted? I'd love to understand the root cause....

[SwissXC90]

Go Tannaton! The more curious an XC90 fault, the more Tannaton wants to know...


Well Done That Man